This invention relates to a method for adjusting a color of a monochromatic image of a liquid crystal display (LCD) and each of LCDs or a monochromatic LCD and monochromatic LCDs, and a medical image display apparatus. More particularly, the invention relates to the technology of enabling adjustment of the color difference between two or more medical monochromatic displays.
Medical image display systems often use monochromatic displays to represent a variety of radiation and other images. The frequently employed method is an extension from the conventional method of examining a plurality of films on a lantern slide and a plurality of monochromatic displays are placed side by side as they individually display an image. It is often pointed out that any difference that exists in color (sometimes called hue or color tone) between monochromatic displays introduces difficulty for the viewer (e.g. a doctor or a radiological technician) to examine the image.
This problem has been pointed out since the time of using monochromatic CRT displays. The color of CRT displays is subject to the constraints at the materials level exemplified by the lot-to-lot difference in the phosphor used in CRT manufacture and, hence, it has been held theoretically impossible to achieve color adjustment, or eliminate the color difference between monochromatic displays.
From various design considerations including smaller size, lighter weight and less power consumption, the CRT display is increasingly supplanted today by a liquid-crystal display, commonly abbreviated as LCD. However, if a plurality of LCDs are placed side by side and used as monochromatic displays, there still occurs the problem of color difference that exists between represented images.
The greatest difference between a CRT display and an LCD lies in the mechanism of light emission. In the CRT display, the phosphor excited by an electron beam emits light on its own (spontaneous luminescence) whereas in the LCD, light produced by illumination with a backlight such as a fluorescent lamp has its transmittance varied by liquid crystal to control brightness.
Because of this difference, the color of the CRT display is already fixed at the time of its manufacture and later adjustment is practically impossible. This is not the case with the LCD and it is by no means impossible to vary the color of a display image by changing the color of the backlight.
The backlight in the conventional common LCDs is an array of multiple cold cathode-ray tubes of about 3 mm in diameter that are so adapted that the emerging light is diffused uniformly. If the backlight itself is adapted to permit color change, the color of the image represented by the LCD becomes variable.